High-capacity current limiter



Jan. 13, 1953 F. MATTHYssE 2,625,626

HIGH-CAPACITY CURRENT LIMITER Filed Dec. 2, 1948 MLM# ATTORNEY Patented Jan. 13, 1953 HIGH-CAPACITY CURRENT LIMITER Irving F. Matthysse, New York, N. Y., assignor t Burndy Engineering Company, Inc., a corpora.-

tion of New York Application December 2, 1948, Serial No. 63,092

(Cl. 20D-120) Claims.

My invention relates to a high capacity limiter for interrupting very heavy fault electrical currents.

It has been found that the common limiter used in the secondary network systems of electric light and power companies has adequate interrupting capacity for most applications of 12o/208 volt three phase alternating current systems. However, in large factories where secondary voltages such as 440 and 550 volts are used these limiters become explosive when interrupting a heavy fault.

For such voltages, the ordinary 600 volt cartridge fuse was found incapable of interrupting faults of 10,000 amperes or more without considerable violence.

There are available fuses of very high interrupting ability for voltages considerably greater than 600 volts but these fuses are not made to carry the continuous currents in the 500 to 1000 ampere range found in 600 volt secondary systems. In addition such fuses are bulky and costly. One form of these high voltage fuses uses multiple silver wires for the fusible element which are enclosed in a glass tube filled with quartz sand. The hot gases from the silver wires are chilled and condensed by the quartz particles thereby limiting the duration of the electric arc. This action is facilitated by the use of many small fusible wires in multiple instead of one large wire.

This principle is very effective in extinguishing the arc rapidly and reducing the pressure in the fuse. However, for large ampere sizes the amount of metal in the fusible section would be proportionately greater resulting in the need for more sand and larger diameter with corresponding wall thicknesses.

There is available a limiter having a metal tube enclosure surrounding a single copper fusible element. To prevent the arc from striking to the container and to reduce the internal pressure this limiter must employ a sufficiently large metal enclosure.

I have found that I can unexpectedly reduce the normal diameter of a limiter having the desired characteristics by combining the metal shell and quartz particles with an arc-proof closure positioned between the metal shell and the quartz particles. The reduction of diameter of the 2 metal shell is thus obtained without any loss of any safety values.

It is therefore the primary object of my invention to provide a limiter of larger capacity having a metal shell of reduced diameter.

Tests have shown that in the foregoing limiter it is necessary that the quartz particles not be permitted to shift causing empty pockets to form which would lessen the effectiveness of the limiter and render it more dangerous. Accordingly further objects of the invention include the provision for preventing the shifting of the quartz particles after iilling, and the prevention of empty pockets in the quartz particle chamber by completely filling the chamber after assembly of all the parts.

Additional objects consist in providing a limiter that is fully sealed to prevent free escape of gases; providing a fusible element that is brazed to its supporting members; in providing a metal cover which is maintained in position on the arcproof enclosure by retaining rings; in providing a limiter in which the quartz particles are added through a central aperture in one of the supporting members; in providing an arc-proof enclosure for the fusible element which is in separable parts to facilitate assembly and which may be sealed and held together by the retaining rings; in further providing the arc-proof enclosure with restricted end portions to prevent Withdrawal of the supporting elements and an outer depressed portion at each end to accommodate the retaining rings; and providing end insulating caps which prevent electrical leakage; and further providing a limiter of economical design and of minimum size.

I accomplish these and other objects and obtain my new results as will be apparent from the device described in the following specification, particularly pointed out in the claims, and illustrated in the accompanying drawing, in which- Fig. 1 is a side view of the improved limiter.

Fig. 2 is a cross sectional View taken along lines 2 2 of Figure 3.

Fig. 3 is a cross sectional view taken along lines 3 3 of Figure 2.

Referring more particularly to the drawing the limiter I0 comprises a pair of terminal supports Il and l2. Each terminal has a tubular portion I3 and I4 and inter-fitting support plugs I and I6 brazed thereto. The external portion I3 of the terminal may be flattened as at I'I and provided with attaching holes I8, while tubular portion I4 receives cable I9 and is indented thereto at 20. It is not intended to limit the invention specifically to the connection illustrated since both ends of the terminal may be attened as for a bayonet type of fuse or both ends may be tubular to connect the limiter between cable ends. The inner ends of support plugs I5 and IS have shoulders 2I and 22 on which is brazed the fusible element 23, a copper sheet having blanked out slots 24 and fusible links 25 and rolled into tubular form. Plug I6 has a longitudinal filling passage 26 extending throughout its length and internally threaded at its outer end to receive closure plug 27.

Surrounding the fusible element 23 and sup-V port plugs I5 and I6 and spaced therefrom lis an arc-proof insulating shell 28, which may be made from a material, such as asbestos-cement compound, having a good resistance to mechanical and heat shocks. The shell may be made of two intertting parts 29 and BIJ as shown in Fig. 3, to facilitate assembly and has a neck portion 3i and 32 which ts around the tubular portions of the terminal and is sealed thereto by means of a high temperature cement 9. The central portion of the shell forms a housing 33 around the fusible element to receive quartz particles 3d which are filled through passage 25 of the plug I3 and flows through slots 24 to completely surround each link 25 of the fusible element and fill the housing 33. The quartz particles during a conditionv of a fault current act to chill and de-ionize the gases from the volatilized fusible element, thus extinguishing the arc and reducing the internal pressure. It is important that the housing is completely lled with the quartz particles to prevent voids between the fusible element and the shell. Filling the housing after the limiter is completely assembled better insures the absence of air pockets which lessen the effectiveness of the limiter. The central portion of the shell 28 surrounding the fusible element. has undercut ribs or radially extending barriers 35 to prevent shifting of the quartz particles.

The outer ends of the shell 28 are constricted I at 35 and 31 to accommodate external threaded retaining rings 38 and 39 and end closure caps 40 and 4i. A tubular enclosure 32, which may be ofv metal or other high strength material to withstand high explosive pressures that arise during fault currents, further acts to reinforce the shell. By providing this reinforcement, the shell 28 may be made with a relatively small diameter and thin wall structure, and still function to prevent the hot gases from contacting the enclosure, which when it is metal might provide a path for the current to prolong and enlarge the arc.

The enclosure 42 is internally threaded at each end to receive the retaining rings 38 and 39 which secures the enclosure to the shell 23. The insulated closure caps I0 and 4I have a central aperture through which the terminals extend and an external flange 43 and dll, the inner portion fitting over the restricted portions 35 and 31 of the shell and cemented thereto, and an outer edge which snugly abuts the ends of the enclosure t2 and provides a resistance to surface electrical leakage. By providing constricted portions 35 and 31 to accommodate the 4 retaining rings and closure caps, all the elements are flush and the outer surface of the limiter is cylindrical in form and free from protuberances.

Besides sealing the shell 28 to the tubular portions I3 and I4 with the high temperature cement 9, the caps QB and i and rings 38 and 39 are sealed to the shell as indicated in Figure 2.

I have thus described my invention, but I desire it understood that it is not confined to the particular forms or uses shown and described, the samev being merely illustrative, and that the invention may be carried out in other Ways without departing from the spirit of my invention and, therefore, I claim broadly the right to employ all equivalent instrumentalities coming within the scope of the appended claims, and by means ofwhich, objects of my invention arer attained and new results accomplished, as it is obvious that the particular embodiments herein shown and described are only some of the many that can be employed to attain these objects and accomplish these results.

I claim:

1. A current limiter comprising a terminal and fusible element assembly having an enlarged central section, an insulating shell made into a plurality of parts having an enlarged central portion forming a housing to enable said enlarged portion of the shell to be mounted over and spaced from the enlarged section of the terminal and fusible element assembly to prevent longitudinal movement of said assembly with respect to said shell, supporting means mounted on said shell to hold the plurality of shell parts together about the terminal and fusible element assembly, said enlarged portion of the shell containing an arc suppressing medium positioned about the enlarged section of the terminal and fusible element assembly, said terminals extending beyond said shell for attachment to a plurality of conductors.

2. The current limiter of claim 1 wherein the insulating shell is divided longitudinally into the plurality of longitudinally separable parts.

3. The current limiter of claim 2, wherein the insulating shell is provided with a plurality of radially extending barriers forming a portion of each part.

4. A current limiter comprising a terminal and fusible element assembly, an insulating shell, and an outer protective enclosure, a pair of conductor terminals positioned one at each end thereof, a fusible element extending between said terey minals and supported thereby, said fusible element being positioned in the insulating s hell to be spaced therefrom, a flowable arc suppressing medium contained within the insulating vshell and surrounding the fusible element, said terminal and fusible element assembly having means for completely filling the insulating shell with the arc suppressing medium from a point outside the assembled insulating shell.

5. A terminal and fusible element assembly comprising an insulating shell, a pair of conductor terminals positioned at each end thereof, a fusible element extending between said terminals and supported thereby, said fusible element being positioned in the insulating shell to be spaced therefrom, a flowable arc suppressing medium contained Within the insulating shell and surrounding the fusibleelement, at least one of said ter-` minals being hollow and having an opening ac: cessible from outside the insulating shell whereby 5 the insulating shell may be completely lled with the are suppressing medium from outside the assembled insulating shell, and means for sealing the opening.

IRVING F. MATTHYSSE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 640,371 Downes Jan. 2, 1900 813,546 Fellenberg Feb. 27, 1906 Number Number Name Date Steinmann Mar. 26, 1907 Weissberg Apr. 7, 1914 Wake Dec. 5, 1916 Stephenson Aug. 29, 1933 Brown May 19, 1936 Hill Oct. 6, 1936 Papp July 7, 1942 Rawlins et al May 22, 1945 Schuck Feb. 3, 1948 FOREIGN PATENTS Country Date Great Britain Feb. 21, 1929 

